Author: mikeh69

I recently bought a table-top mini pillar drill, sold in UK by AIM Tools as Katsu 100080, and added a small cross-table (Katsu 402188 from AIM Tools, AKP-201 on Alibaba) to create a precision drilling setup. Total cost only £144, and I’m very pleased with the result:

The drill has no noticeable run-out – in contrast to a full-size pillar-drill, the motor moves up and down with the quill, and there is no extending spline (which seems to be the problem with cheap pillar-drills I’ve used), though this does limit the rise/fall (and hence maximum drilling depth) to only 25mm. The chuck only holds drills up to 6.5mm, so precision jobs is what it’s made for! It’s powered by a sewing-machine motor rated at only 100W, but it did OK drilling 3mm holes in cast iron, you just have to take your time (again, precision jobs…).

The base of the mini-drill is cast iron, and I was expecting problems in drilling and tapping the four fixing holes for the cross-table, but no – didn’t encounter any hard spots, and it tapped more easily than aluminium. I didn’t apply any lubricant to the tap, and the waste (quite fine iron filings) simply dropped out of the hole rather than clogging it.

The action of the cross-table is superb – backlash is minimal, but the gib screws are not insanely tight (in marked contrast to a £50 cross-vice I’ve used, which needed constant tweaking of the gib screws). Weighing in at 11kg, it will definitely keep the drill steady!

Since the tapped holes in the drill base had gone so well, I drilled and tapped some M4 holes into the rear face of the cross-table (same story, easy peasy!) to attach a flat plate, creating a “lip” along the rear edge of the table for easy alignment of rectangular work-pieces:

Another possible enhancement for the future is to add a taller drill column – as supplied, it’s only just high enough to give useable clearance between the chuck and the table. It appears to be made from any-old steel tube, turned to 32.5mm diameter. I’ll probably use solid 35mm round bar – luckily I know a man with a lathe…

The use of RF jammers or blockers by criminals to break into cars is spreading – this BBC News report is from December 2016, and this from May 2017. How can you protect yourself? This Hackaday post describes a simple “yes/no” receiver to detect jamming on the car-keyfob frequency. Better than nothing, but it doesn’t tell you whether you’re right in the crims’ target zone, or half a mile away.

I had been messing around with a cheap RTL-2832 DVB-T dongle, and it seemed like it should be quite straightforward to use it as a direction-finding/homing receiver to give a “warmer/colder” indication and work out exactly where a jammer was being used. As it turned out, the software-radio bit was quite easy – the tricky part was making Linux generate simple beep-tones to indicate the signal-strength! (anyone else fondly remember the ZX Spectrum Basic BEEP command?)

Jammer-Detect running on a laptop – the bar-graph extends across the screen and changes colour to indicate RSSI on every “sample”, while beep-tones about play once a second indicating the maximum signal-strength received in the last 32 samples.

The main part of the code is written in Python 3, with the RF-power calculation implemented in C for efficiency. It can be run on a laptop, but the real fun starts when you install it on a Raspberry Pi that fits in your pocket – a single earphone feeds you audio tones that indicate “warmer / colder”, and you can then walk or drive around an area to track down the source of a jamming signal.

How to build it

Create a Raspbian bootable micro-SD card by following the instructions here. Raspbian Lite will boot faster than the “With Desktop” version, so I used that.

Put the micro-SD card into the Pi, and connect a monitor, USB keyboard, network cable and power-supply. When the Pi finishes booting and shows a “raspberrypi login:” prompt, log in as “pi”, “raspberry” and execute the following commands to install required packages and download the source-code from Github:

(and log in again as pi – raspberry). The Udev rules file also includes an “unplug” rule that tells the Pi to shut down in an orderly fashion if the DVB-T dongle is unplugged – a cleaner solution than just pulling the power!

Now try out the program. The first time it runs, it will take a minute or so to generate the audio-tone data and save it to a file. On subsequent runs, the tone-data will be loaded from the file, which is much quicker. Plug in your DVB-T dongle, and type:

sudo amixer cset numid=1 100%

to set the audio-output volume to 100%, then:

cd jamdet/JammerDetect/src
python3 jammer_detect_main.py

(Press Ctrl – C to break out of the program).

To make the program run automatically when the Pi boots, do:

crontab -e

(which opens the “cron table” file in an editor), and to the end of the file add this line:

(Press Ctrl-X, Y to save and exit from the Nano editor). This runs a version of the program that has no graphical display, just the audio tones, because an automatically-run program has no console to send graphics to.

sudo reboot

and listen to the earphone…

The centre-frequency of the band is currently hard-coded to 433.92MHz (the European car-keyfob band), but the Python script (jammer_detect_main.py or jammer_detect_no_ui.py) can simply be edited to change this to any frequency that the DVB-T dongle is able to tune to – see this page for tuning ranges of various dongles.

The antenna doesn’t have to be particularly “good”, or well-matched to the frequency of interest – if a jammer is putting out enough power to be effective, your receiver won’t need great sensitivity to pick it up!

Next bit of work might be to improve the large-area survey (driving around a city) – go back to running on a laptop, add a USB GPS puck and keep a log of signal-strength against lat/long, then generate a “heat-map” KML file to display on Google Earth…

Acknowledgements: Thank you to Steve Markgraf for LibRtlSdr, and to “Roger” for the Python bindings. I’m standing on the shoulders of giants…

I mentioned earlier the trouble I had generating simple audio tones. The difficulty was in preventing unpleasant clicks at the start and end of a “beep”. It turned out to be necessary to fade IN, as well as fade out, each tone. audio_tones.py generates sets of samples for PortAudio to create beeps at semitone intervals – it’s completely self-contained and can be used in other projects.

This cable is available for £7-10 from a couple of EBay sellers (search for “Clansman H-39 handset wiring” or “Clansman cord assembly”) , and could be useful for connecting up Racal Clansman or Cougar kit.

As you’d expect for a mil-spec item, it’s very well made, including a nylon strain-relief cord tied off to a steel toggle-pin inside the connector. But… there is a white wire, which is terminated with the same type of crimp as the other coloured wires, but at the plug end of the cable it’s trimmed off and not connected to anything! What a massive D’OH!

It’s very fiddly, but I was able to open up the plug and solder a new piece of wire from pin C to the end of the white wire. (You need to use large pliers/plumbing grips and a rag to avoid scratching the paint too badly, as there is locking compound applied to the threads.) Getting the connector reassembled with the toggle-pin in the right place is fun (not). With DC power connected through, it becomes a lot more useful!

Alternatively, Ebay seller MartinJarvisMultiband has two versions of the plug for sale (message him if none currently listed), and Lapp cable type 0034307 LIYCY from Ebay seller 123dls-industrial works quite well with it (though doesn’t have the nylon strian-relief cord).

I’m doing some work to develop a low-cost desktop Electronic Video Magnifier system to allow people with impaired vision to view hardcopy documents on a computer monitor, with functions to adjust brightness and contrast, change colour scheme, zoom in and out etc. Commercial desktop EVMs are available, but cost in the thousands of pounds/dollars. This system will use an £80 USB document camera, a user’s existing PC and monitor (or e.g. a Raspberry Pi and a TV) and free open-source software.